Nile Red is intensely fluorescent in a lipid-rich environment while it has minimal fluorescence in aqueous media. Whereupon, three neutral red/near-infrared fluorescent dyes 1a-1c with good water solubility were synthesized by introducing nitrogen atoms into the 2, 3 and 4 positions of Nile Red in order to improve the biocompatibility in this paper. Optical testing showed that the maximum absorption wavelengths of 1a-1c were in the range of 525–617 nm, while the maximum emission ones located at 584–668 nm in different solvents. When the solvent polarity (Δf) was reduced from 0.316 to 0.020, the maximum absorption wavelengths of 1a-1c were blue-shifted by 73–97 nm, and the fluorescence intensities were enhanced by 32–44 folds. Meanwhile, excellent linear relationships between the fluorescence lifetimes, absolute fluorescence quantum yields of 1a-1c and Δf (0.229–0.307) were established with high correlation coefficients (R² = 0.98–0.99). In addition to excellent low toxicity and mitochondrial targeting properties, 1a-1c were able to detect polarity changes in models of inflammation induced by Lipopolysaccharide at 50 nM. Furthermore, based on the significant mitochondrial polarity differences between cancer and normal cells, 1a-1c had the ability to differentiate them. And 1a-1c also were capable of real-time monitoring mitochondrial polarity during starvation or rapamycin-induced autophagy. Overall, the excellent optical properties and biocompatibility of aza-Nile Red (1a-1c) suggest that they have great potential in studying mitochondrial physiology and pathological biological processes.

中文翻译：

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基于 aza-Nile Red 的荧光探针，用于可视化线粒体极性波动


尼罗红在富含脂质的环境中具有强烈的荧光，而在水性介质中的荧光最小。为此，通过在尼罗红的 2、3 和 4 位引入氮原子，合成了三种具有良好水溶性的中性红/近红外荧光染料 1a-1c，以提高本文的生物相容性。光学测试表明，1a-1c 的最大吸收波长在 525-617nm 范围内，而最大发射波长位于 584-668nm 处，处于不同的溶剂中。当溶剂极性 （Δf） 从 0.316 降低到 0.020 时，1a-1c 的最大吸收波长发生了 73-97nm 的蓝移，荧光强度提高了 32-44 倍。同时，荧光寿命、1a-1c 和 Δf 的绝对荧光量子产率 （0.229–0.307） 之间建立了极好的线性关系，具有高相关系数 （R² = 0.98–0.99）。除了优异的低毒性和线粒体靶向特性外，1a-1c 还能够检测 50 nM 脂多糖诱导的炎症模型中的极性变化。此外，基于癌症细胞和正常细胞之间显着的线粒体极性差异，1a-1c 具有区分它们的能力。1a-1c 还能够在饥饿或雷帕霉素诱导的自噬期间实时监测线粒体极性。总体而言，氮杂-尼罗红 （1a-1c） 优异的光学特性和生物相容性表明它们在研究线粒体生理学和病理生物过程方面具有巨大潜力。